Jet fuel composition



United States This invention relates to a novel jet fuel and more particularly it is concerned with providing a hydrocarbon jet fuel containing minor amounts of two particular additives for the purpose of imparting to the fuel improved high-temperature stability.

.Modern jet engines of the jet or turbo-jet type impose severe restrictions on the type of fuels which may be satisfactorily employed in their operation. In jet engines which include a compressor, a combustor, and a turbine wheel or rotor, the fuel is mixed with compressed air and then burned in the combustor chamber. The heated air and products of combustion accelerate against the turbine wheel blades to drive the compressor and are then released backward from the engine, producing the force or reaction which drives the engine and aircraft forward. Since heavy duty jet engines operate at shaft speeds of about 8000 r.p.m., shaft bearings must be provided with lubricants which not only reduce friction but carry away the engine and frictional heat. In the supersonic air-speed region where most military jets are designed to operate, conventional air-cooled lubricating oil heat exchangers are useless. Consequently, the growing trend is to use the fuel supply as a coolant for the lubricating oil.

In oil-fuel heat exchangers, the fuel is subjected to quite high temperatures, on the order of 400-500 F. At these conditions, if the fuel is thermally unstable and particularly if it is susceptible to oxidative gum formation, the heat exchanger may become fouled and inefiective and as a result oil temperatures may rise and bearing failures can occur. Moreover, suspended gum and soluble gum which form in the exchanger are carried downstream with the fuel, where they plug fuel filters and nozzles. Ultimately, engine roughness, cycling, reduced performance, and combustor warping may result from such plugging. Even complete engine flame-out may occur.

'Unfortunately, most conventional oxidation inhibitors are oflittle or no value in stabilizing jet fuels at the 400-500 F. exchanger temperatures; in some cases, conventional inhibitors actually decrease thermal stability. It is therefore a primary object of the present invention to provide a fuel which is stable under the extremely severe conditions of use in jet-type engines, and to enable the use of hydrocarbon jet fuels which, in the absence of additives of the invention, would be too unstable from the standpoint of deposits formed in the heat exchanger and inlet system.

-A jet fuel, to which there is incorporated the additive combination of the invention, consists chiefly of a liquid hydrocarbon fluid boiling in the range of about 150 to 650,F. usually'in the range of about ISO-600 F. Fuels meeting the standards of JP-4 (specification MI-LF 5624D) are typical examples, and have a Reid vapor pressure between 2.0 and 3.0, a maximum evaporated point of 250 F., a maximum end point of 550 F., a freezing point of 76.0 F., a specific gravity of between 0.747 and 0.825, and a maximum bromine number (related to the allowable concentration of olefins therein) of 33.0. JP-4 fuels may contain a maximum of 25 volume percent aromatics and can have a 16 hour accelerated gum content of 14 mg./ 100 ml.; they may contain up to 0.40 weight percent sulfur, including up to 0 0.001% mercaptans. To such liquid hydrocarbon there is added, in accordance with the invention, amounts ef-' fective to at least partially inhibit gum deposition and filter plugging, of (a) a hydrazone and (b) an alkali metal-containing hydrolyzed reaction product of a phosphorous sulfide and a normally liquid hydrocarbon. The

hydrazone is especially effective for reducing gum formation in the oil-fuel heat exchanger but, by itself, does not keep gum sediments in suspension and, if used alone, would not prevent filter plugging. On the Other hand, the alkali-metal-containing phosphorous sulfide-hydrocarbon reaction product is, by itself, ineifective in reducing gum formation in the exchanger, but does keep gum in suspension, thus preventing fuel filter plugging. Hence the combination of the two additives in accordance With the present invention provides a hydrocarbon jet fuel which is inhibited against both exchanger fouling and filter plugging.

The amounts of each additive which are added to a particular jet fuel depend both on the temperature in the oil-fuel heat exchanger and on the inherent stability of the fuel. Where the fuel is highly unstable, particularly when derived from thermally cracked petroleum hydrocarbons, both additive concentrations may be relatively high, while an essentially virgin jet fuel requires very little of either. Ordinarily, the amount of alkalimetal phosphorus sulfide-hydrocarbon reaction product may range from as little as 0.0001 volume percent to about 5 volume percent based on hydrocarbon fuel, but. it is usually in the range of about 0.001 to 0.5%, pref erably between 0.01 to 0.05% for the average JP-4 or' JP-5 fuel. The amount of hydrazone may be as little as 0.001 to as much as about 5 volume percent, preferably between 0.01 to 0.05%. Since hydrazones may, vary considerably in molecular weight, the required" amounts thereof may be defined on the basis of moles of additive per liter of hydrocarbon and, in these terms, there may be used 0.0001 to 0.1, preferably 0.001 to" 0.03 mole of hydrazone per liter (M/l.) of jet fuel. As claimed in co-pending application S.N. 625,230 filed by B. L. Mickel et a1. November 30, 1956, now abandoned; an alcohol or phenol type solubilizer for the hydrazone.

may additionally be employed.

Hydrazine is H NNH while phenylhydrazine is Hydrazones are reaction products ofhydrazine, alkyli hydrazines or phenylhydrazine with carbonyl compounds; i.e. ketones or aldehydes. Hydrazones within the scope:

of the present invention thushave theformula C=NN R2/ s and R1R2CHINNC6H5. hydes which may be reacted with hydrazine or phenylhydrazine to form hydrazones are acetaldehyde,propion aldehyde, butyraldehyde,

acetaldehyde, dimethyl ethyl acetaldehyde, and benzalde-" hyde. Suitable ketones for the preparation of hydrazones isobutyraldehyde,

include acetone, methyl ethyl ketone, diethyl ketone, di'-" isopropyl ketone, hexyl methyl ketone, and acetophenone.

. Hydrazones may either be prepared from the correspond;

ing aldehyde or ketone by mixing with hydrazine, an

Patented Aug. 21, 1962 trimethyl" 3 alkyl hydrazine, or phenylhyd'razine, or may be prepared indirectly by oxidation of N-bromoamines with silver oxide or by reduction of azines. There is some variation in the suitability of the various hydrazines, and the ketone-derived hydrazones, particularly those such as diisobutyl hydrazone which are derived from unsubstituted hydrazine, appear to exhibit superior properties for inhibiting exchanger fouling. A mixture of two or more hydrazones may be employed.

The alkali metal-phosphorous sulfide-hydrocarbon additives are well known and widely used as gasoline and motor fuel additives. In the preparation of the phosphorus sulfide-hydrocarbon reaction product, the hydrocarbon is reacted with a phosphorus sulfide, such as P P 8 P 8 or other phosphorus sulfides, and preferably phosphorus pentasulfide, P 8

The hydrocarbon constituent of this reaction is suitably a hydrocarbon such as is described in detail in U.S. 2,316,- 080, 2,316,082, and 2,316,088, each issued to Loane et al. on April 6, 1943.

While the hydrocarbon constituent of this reaction can be any of the type hereinafter described, it is preferably a mono-olefin hydrocarbon polymer resulting from the polymerization of low molecular weight mono-olefinic hydrocarbons or isomono-olefinic hydrocarbons, such as propylene, butylenes, and amylenes or the copolymers obtained by the polymerization of hydrocarbon mixtures containing isomono-olefins and mono-olefins or mixtures of olefins in the presence of a catalyst, such as sulfuric acid, phosphoric acid, boron fluoride, aluminum chloride or other similar halide catalysts of the Friedel-Crafts type.

The polymers employed are preferably mono-olefin polymers or mixtures of mono-olefin polymers and isomono-olefin polymers having molecular weights ranging from about 150 to about 50,000 or more, and preferably from about 300 to about 10,000. Such polymers can be obtained, for example, by the polymerization in the liquid phase of a hydrocarbon mixture containing mono-olefins and isomono-olefins such as butylene and isobutylene at a temperature of from about 80 F. to about 100 F. in the presence of a metal halide catalyst of the Friedel- Crafts types such as, for example, boron fluoride, aluminum chloride, and the like. In the preparation of these polymers there may be employed, for example, a hydrocarbon mixture containing isobutylene, butylenes and butanes recovered from petroleum gases, especially those gases produced in the cracking of petroleum oils in the manufacture of gasoline.

Essentially parafiinic hydrocarbons such as bright stock residuums, lubricating oil distillates, petrolatums, or paraflin waxes, may be used. There can also be employed the condensation products of any of the foregoing hydrocarbons, usually through first halogenating the hydrocarbons, with aromatic hydrocarbons in the presence of anhydrous inorganic halides, such as aluminum chloride, zinc chloride, boron fluoride, and the like.

Other preferred olefins suitable for the preparation of the herindescribed phosphorus sulfide reaction products are olefins having at least 20 carbon atoms in the molecule of which from about 13 carbon atoms to about 18 carbon atoms, and preferably at least 15 carbon atoms, are in a long chain. Such olefins can be obtained by the dehydrogenation of paraflins, such as by the cracking of paraffin waxes or by the dehalogenation of alkyl halides, preferably long chain alkyl halides, particularly halogenated parafiin waxes.

Also contemplated within the scope of the present invention are the reaction products of a phosphorus sulfide with an aromatic hydrocarbon, such as for example, benzene, naphthalene, toluene, xylene, diphenyl and the like or with an alkylated aromatic hydrocarbon, such as for example, benzene having an alkyl substituent having at least four carbon atoms, and preferably at least eight carbon atoms, such as long chain paraflin wax.

The phosphorus sulfide-hydrocarbon reaction product can be readily obtained by reacting a phosphorus sulfide, for example P 8 with the hydrocarbon at a temperature of from about 200 F. to about 500 F., and preferably from about 200 F. to about 400 B, using from about 1% to about 50%, and preferably from about 5% to about 25% of the phosphorus sulfide in the reaction. It is advantageous to maintain a non-oxidizing atmosphere, such as for example, at atmosphere of nitrogen above the reaction mixture. Usually, it is preferable to use an amount of the phosphorus sulfide that will completely react with the hydrocarbon so that no further purification becomes necessary; however, an excess amount of phosphorus sulfide can be used and separated from the product by filtration or by dilution with a hydrocarbon solvent, such as hexane, filtering and subsequently removing the solvent by suitable means, such as by distillation. If desired, the reaction product can be further treated with steam at an elevated temperature of from about F. to about 600 F.

The phosphorus sulfide-hydrocarbon reaction product normally shows a titratable acidity which is neutralized by treatment with a basic reagent. The phosphorus sulfide-hydrocarbon reaction product when neutralized with a basic reagent containing a metal constituent is characterized by the presence or retention of the metal constituent of the basic reagent. Prior to neutralization the reaction product can be hydrolyzed and clayed to remove inorganic acids of phosphorus as described in U.S. 2,688,612 issued to R. W. Watson September 7, 1954.

The neutralized phosphorus sulfide-hydrocarbon reaction produce can be obtained by treating the acidic reaction product with a suitable basic compound, such as hydroxide, carbonate, oxide, or sulfide of an alkali metal, such as for example, potassium hydroxide, sodium hydroxide, sodium sulfide, lithium hydroxide rnonohydrate, etc. The neutralization of the phosphorus sulfide-hydrocarbon reaction product is carried out preferably in a non-oxidizing atmosphere by contacting the acidic reaction product either as such or dissolved in a suitable solvent, such as naphtha, with a solution of the basic agent. As an alternative method the reaction product can be treated with solid alkaline compounds, such as KOH, NaOH, Na CO K CO Li O, LiOH, Na S, and the like, at an elevated temperature of from about 100 F. to about 600 F.

The test commonly employed for establishing the efficacy of additives for jet fuels is the so-called ERDCO fuel coker test described in ASTM Standards on Petroleum Products, pp. 1059-1082, November 1957. This coker was designed by the Pratt-Whitney Division of United Aircraft and simulates the fuel system of the 1-57 military jet engine. According to this test, the thermal stability of a fuel is measured both in terms of the gum or coke which deposits on a heat exchanger surface, and in terms of the rate at which suspended gum clogs a sintered stainless-steel filter downstream. -In this test pro.- cedure the fuels are heated in an annular preheater to 400 F., and the filter temperature is held at about 500 P. so that the fuel temperature at the filter is of the order of about 440 F. The fuel sample is air saturated immediately preceding the run, and the fuel flow rate is from four to six pounds per hour. Results are expressed in terms of minutes necessary to incur a pressure drop of 25 inches mercury across the fuel filter and, at the end of a five hour test period, by the visual appearance of gum deposits on the heat exchanger tube. Observations of the latter are based on an estimated percentage of total tube area covered by gum, and by rating the thickness of the deposit as zero for no deposit, one for light to light tan, two for medium tan, and three for heavy brown deposits. The product of percentage area and deposit thickness is taken as the total gum deposition during the five hour test period.

When a commercial JP-4 jet fuel, containing 5% by volume of thermally cracked heavy naphtha to make it more susceptible to gum formation, is tested in the ERDCO tester, both with and without the additives of the invention, the results shown in the following table are obtained. The hydrazone is the hydrazone of diisobutyl ketone, and the other additive is the potassiumneutralized steam hydrolyzed reaction product of phosphorus pentasulfide with a polybutene having a molecular weight of about 900-100.

Run number 4 shows that JP-4, containing only the approved amount of a metal deactivator and an antioxidant, deteriorates rapidly under conditions of the ERDCO test. In run number 3, with diisobutyl ketone hydrazone alone, heat exchanger deposits are greatly reduced but only a slight improvement in filter plugging time is noted. With only the neutralized P S -hydrocarbon reaction product, however, there is actually a slight increase in heat exchanger deposit over the JP-4 of run 4, but more than ten-fold improvement in filter pressuredrop time. In run number 1 in accordance with the invention, a mixture of the two additives is effective both in reducing heat exchanger deposits and in providing a vastly improved performance of the filter.

The foregoing test data demonstrate that by adding described amounts of hydrazone and alkali metal-containing phosphorus sulfide-hydrocarbon reaction product to a liquid hydrocarbon jet fuel, degradation and insolubles formation are at least partially inhibited and the fuel side of a jet engine is maintained in cleaner condition with more effective heat exchange and less pressure drop than would be possible in the absence of either or both of the jet fuel additives.

The additive combination of the present invention is also applicable to hydrocarbons used as rocket fuel-s where the same requirements of short-time high temperature stability must exist. Liquid fuel rockets may employ circulation of the incoming hydrocarbon fuel around the exhaust nozzle before the fuel is injected into the combustion chamber. Should gum or coke deposition occur in this service, the nozzle would over-heat and ultimately cause destruction of the rocket engine and perhaps the rocket vehicle itself. Addition of the prescribed additives to such fuels renders them more able to withstand thermal and oxidative degradation when exposed to such conditions.

We claim:

1. A hydrocarbon fluid of the jet fuel boiling range normally tending to cause heat exchanger gum deposition and filter plugging in jet engines, and containing, in amounts effective to at least partially inhibit said gum deposition and plugging, of (a) from about 0.001% (vol.) to about 5.0% (vol) a hydrazone of the formula where R R and R are each selected from the group consisting of hydrogen atoms, alkyl radicals of 1-6 carbon atoms each, and phenyl radicals, and from about 0.0001% (vol) to about 5% (vol.) of (b) an alkali metal containing neutralized reaction product of a phosphorus sulfide and a normally liquid hydrocarbon obtained by reacting from about 1% to about 50% of a phosphorus sulfide with the normally liquid hydrocarbon at a temperature of from about 200 F. to about 500 F, hydrolyzing the resultant reaction product and neutralizing the hydrolyzed reaction product with a basic alkali metal compound.

2. The hydrocarbon fluid of claim 1 in which the hydrazone is an alkyl hydrazone.

3. The hydrocarbon fluid of claim 1 in which the hydrazone is diisobutyl hydrazone.

4. The hydrocarbon fluid of claim 1 in which the hydrazone is phenyl hydrazone.

5. The hydrocarbon fluid of claim 1 in which the hydrazone is an alkyl phenyl hydrazone in which the alkyl radicals contain from 1 to 6 carbon atoms.

6. The hydrocarbon fluid of claim 1 in which the alkali metal is potassium and the normally liquid hydrocarbon is a normally liquid olefin.

7. In the method of operating jet engines having oilfuel heat exchangers, the improvement which comprises supplying to said engines a hydrocarbon fuel containing (a) from about 0.001 to about 5 volume percent of a hydrazone of the formula \C=NN/ Rz Ra where R R and R are each selected from the group hydrogen atoms, alkyl radicals of 1-6 carbon atoms each, and phenyl radicals, and (b) from about 0.0001 to about 5 volume percent of an alkali metal containing neutralized reaction product of a phosphorus sulfide and a normally liquid hydrocarbon obtained by reacting from about 1% to about 50% of a phosphorus sulfide with the normally liquid hydrocarbon at a temperature of from about 200 F. to about 500 F., hydrolyzing the resultant reaction product, and neutralizing the hydrolyzed reaction product with a basic alkali metal compound.

8. The method of claim 7 in which the hydrazone is diisobutyl hydrazone and the alkali metal containing reaction product of a phosphorus sulfide and a normally liquid hydrocarbon is the potassium containing hydrolyzed reaction product of a phosphorus sulfide and an olefin polymer.

References Cited in the file of this patent UNITED STATES PATENTS 2,316,079 Loane et al. Apr. 6, 1943 2,316,080 Loane et al. Apr. 6, 1943 2,316,087 Gaynor et al. Apr. 6, 1943 2,560,542 Bartleson et al July 17, 1951 2,942,957 Wojcik June 28, 1960 OTHER REFERENCES Byrkit et al.: Ind. and Eng. Chem, vol. 42, pp. 1862- (September 1950).

Chem. and Eng. News, pp. 4502, 4569 (October 24, 1955). 

7. IN THE METHOD OF OPERATING JET ENGINES HAVING OILFUEL HEAT EXCHANGERS, THE IMPROVEMENT WHICH COMPRISES SUPPLYING TO SAID ENGINES A HYDROCARBON FUEL CONTAINING (A) FROM ABOUT 0.001 TO ABOUT 5 VOLUMES OF A HYDRAZONE OF THE FORMULA 